SOLUTION: The number of diagonals d in a polygon with n sides is given by the formula d=n^2-3n/2. If the polygon has 90 diagonals, how many sides does it have?

SOLUTION: The number of diagonals d in a polygon with n sides is given by the formula d=n^2-3n/2. If the polygon has 90 diagonals, how many sides does it have?

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Question 213949: The number of diagonals d in a polygon with n sides is given by the formula d=n^2-3n/2. If the polygon has 90 diagonals, how many sides does it have?
Answer by HyperBrain(694) (Show Source): You can put this solution on YOUR website!
Using the formula you've given,
n^2-3n/2=90
So,
n^2-3n=n(n-3)=180=15(12); note that 12=15-3
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So, the polygon has 15 sides.
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